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Alternating Currents
ALTERNATING CURRENT What Are Alternating Currents? Alternating Current, or AC, is a type of electrical current that constantly gets reversed back and forth through it's circuit in a repetitive,cyclical pattern; unlike a direct (DC) current, which always remains constant. Generally, the normal wave form of an AC circuit is a sine wave, as this is the most efficient way to transmit energy. AC power is what provides electricity to your home or buisness. If you are driving around the countryside and you see those gigantic power lines, they are transmitting electricity from power plants to your home, powering your T.V, radio, lights, computer, and other appliances. "Alternating Currents" History The first delivery system for an Alternating Current was called an Induction Coil, which was a precusor to the modern-day transformer, was designed by William Stanley Jr. The modern system was designed between 1881 and 1889 by Nikola Tesla, George Westinghouse, Lucien Gaulard, John Gibbs, and Oliver Shallenger. The systems invented by the above people overcame many of the limitations imposed by using Direct Current, or DC. The first ever long-distance transmission of AC took place near Telluride Colorado in 1891, followed a few months later by a successful transmission in Germany. Although poineers in electricity distribution such as Thomas Edison opposed AC, Alternating Current eventually became the primary method of delivering electricity. Difference Between AC and DC Electric current is made from tiny particles called Electrons which are negatively charged particles that can move around inside a circuit. There are also Protons, which are tiny postively charged particles, and are different from Electrons in that they do not move, which is why Electrons form the current. Since opposites attract, Electrons in a circuit will move toward a positively charged area, through the medium of something like a metal wire.In a DC generator, like a battery, the electrons rush through the wire to the positively charged end, as they are pushed out of the negative side. With an AC generator, a slightly different configuration alternates the push and pull of each side of the circuit. Thus the electricity in the wire moves in one direction for a time and then reverses its direction when the generator configuration is in a different position. See the link below for a motion-diagram of the electron movement in an AC coductor. http://www.school-for-champions.com/science/ac.htm AC electricity alternates back and forth about 50 or 60 times a second, which is designated as 50 or 60 Hertz. The characteristic that makes Altenating Current different from Direct Current, is that a transformer can actually alter the wavelength, and thus the frequency, of an AC wave, which is why AC is the primary form of electricity distribution, as it is so adaptable in it's frequency Mathematics of Alternating Current Alternating Current is normally associated with (gasp) alternating voltages. AC voltage V can be described in this equation: v(t)=Axsin(2pi(ft)) Where A is the Amplitude in volts F is the frequency in Hertz T is the time in seconds The high-to-low value of an AC voltage is defined as the difference between its positive high and its negative low. Since the maximum value of sin(x) is +1 and the minimum value is −1, an AC voltage swings between +A and −A. The high-to-low voltage, written as VP-P, is therefore (+A) − (−A) = 2 × A. References http://www.school-for-champions.com/science/ac.htm http://www.ndt-ed.org/educationResources/HighSchool/Electricity/alternatingcurrent.htm http://engineering.wikia.com/wiki/Alternating_current Regents Questions 80. In a transformer, two coils of wire are wound around a common iron core. To operate properly, the transformer requires an alternating-current source connected to the primary coil a direct-current source connected to the secondary coil more turns in the primary coil than in the secondary coil more turns in the secondary coil than in the primary coil